For many years terahertz receivers and imagers have been used in fields of study in astronomy and chemical sciences for high-resolution spectroscopy and remote sensing areas. In recent years, there has been significant research devoted to Terahertz technology. Because of some of its unique properties it is emerging as an attractive tool for a wider range of applications such as security screening (due to its ability to penetrate through clothing, plastic and packaging materials with higher resolution than microwaves and mm-waves) (See for example, P. H. Siegel, “Terahertz technology,” IEEE Trans. Microw. Theory Tech., vol. 50, no. 3, pp. 910-928, 2002), noninvasive medical imaging (lower scattering compared to optics, contrast in water absorption and tissue density and safe due its nonionizing photon energies) (see, for example, P. H. Siegel, “Terahertz technology in biology and medicine,” IEEE Trans. Microw. Theory Tech., vol. 52, no. 10, pp. 2438-2447, 2004; J-H Son, “Terahertz electromagnetic interactions with biological matter and their applications,” J. Appl. Phys. 105, 102033, 2009), spectroscopic studies and label-free biosensing (see for example, P. H. Bolivar, et al., “Label-free probing of genes by time domain terahertz sensing,” Phys. Med. Biol., vol. 47, no. 21, pp. 3815-3821, November 2002), contraband detection (See, for example, R. Appleby and H. B. Wallace, “Standoff Detection of Weapons and Contraband in the 100 GHz to 1 THz Region,” IEEE Trans. Antennas Propag., vol. 55, no. 11, pp. 2944-2955, November 2007), and industrial and process control. Current THz detector technology comprise discrete and custom devices, which are often bulky and expensive, while not sensitive enough at room temperature. They can be optics-based (such as nonlinear crystals or electro-optic samplers), calorimetric detector technologies (such as bolometers, Golay cells, pyroelectric detectors which are limited by thermal-time constants for their use in video-rate imaging), or solid-state hybrid III-V MMICs (which have higher cost and are less amenable to integration).
FIG. 1A through FIG. 1D illustrate some typical THz detector technology currently in use for astronomical sciences. Comprehensive articles on this subject include P. H. Siegel and R. J. Dengler, “Terahertz heterodyne imaging part I: Introduction and Techniques,” Intl. Jour. Infrared Millimeter Waves., vol. 27, no. 4, pp. 465-477, April 2006; and P. H. Siegel and R. J. Dengler, “Terahertz heterodyne imaging part II: Instruments,” Intl. Jour. Infrared Millimeter Waves., vol. 27, no. 5, pp. 631-655, May, 2006. The important figure of merits for a detector are Responsivity (Rv) and Noise-equivalent-power (NEP). Responsivity is defined as the change in output DC voltage with a unit change in input RF power. NEP is defined as the input power for which the signal-to-noise ratio is unity for an integration time of 1 second.
Prior work and contemporary work have demonstrated the feasibility of silicon technology for THz detection. See, for example, Erik Ojefors et al., “A 820 GHz SiGe Chipset for Terahertz Active Imaging Applications,” ISSCC Dig. Tech. Paper, pp. 224-225, February 2011; E. Ojefors, U. R. Pfeiffer, “A 650 GHz SiGe Receiver Front-End for Terahertz Imaging Arrays”, ISSCC Dig. Tech. Papers, pp. 430-431, February 2010; H. Sherry et al., “Lens-Integrated THz Imaging Arrays in 65 nm CMOS Technologies,” RFIC Symp. Dig., pp. 1-4, June 2011; and F. Schuster et al., “A Broadband THz Imager in a Low-Cost CMOS Technology,” ISSCC Dig. Tech. Papers, pp. 42-43, February 2011. However they can be power-intensive (>300 mW/pixel), require high-resistivity substrates (>1 KΩ-cm) substrates, or use modifications such as silicon lenses or substrate thinning. The main reason necessitating the use of these modifications is the low efficiency of on-chip receiving antennas.
There is a need for improved Terahertz imagers and imaging systems.